This animation shows the motion of a white dwarf star passing in front of a distant background star. During the passage, the faraway star appears to change its position slightly, because its light path has been altered by the white dwarf's gravity.

When the white dwarf Stein 2051 B passed in front of a background star, the distant star's light was offset by only about 2 milliarcseconds from its actual position. This deviation is so small that it is equivalent to observing an ant crawl across the surface of a quarter from 1,500 miles away. From this measurement, astronomers calculated that the white dwarf's mass is roughly 68 percent of the sun's mass.

White dwarfs are the burned-out remnants of normal stars. Stein 2051 B is named for its discoverer, Dutch Roman Catholic priest and astronomer Johan Stein. It resides 17 light-years from Earth. The background star is about 5,000 light-years away.